Ammonium nitrate composition containing combustion catalyst system with an n-aminoalkyl-morpholine



Unite States lml This invention relates to ammonium nitrate-type cornpositions and particularly a catalyst system for promoting the combustion of ammonium nitrate-containing compositions.

An object of the invention is an ammonium nitrate composition. A particular object of the invention is an ammonium nitrate composition having a very high burning rate. A further object is an ammonium nitrate composition whose burning rate is relatively insensitive to variations in burning chamber pressure. Other objects will become apparent in the course of the detailed description.

It has been found that an eminently suitable ammonium nitrate-type composition for rocketry usage is obtained with ammonium nitrate as the predominant component, between about 10 and 40 weight percent of oxidizable organic material, between about 0.5 and 8 weight percent of a Prussian blue and between about 0.5 and 8 weight percent of N-aminoalkylmorpholine having 1-4 carbon atoms in the alkyl portion.

The combustion catalyst system used in the composition of the instant invention contains a Prussian blue, such as insoluble or soluble Prussian blue and an N-amin-oalkylmorpholine having 1-4 carbon atoms in the alkyl portion. Sumcient catalyst must be introduced into the composition to promote the burning of the composition. The amount of catalyst used is also influenced by the rate of burning desired. The more catalyst present the faster the combustion of the composition. It is to be understood that the burning rate is also affected by the particular oxidizable organic material present. In general, the composition will contain between about 0.5 and 8 weight percent of each member of the system. (Hereinafter all percentages are to be understood as weight percent.) With the thermoplastic matrix former-s or binders obtained from polyvinyl resins and oxygenated hydrocarbon plasticizers therefor between about .1 and 6% of each member produces satisfactory burning rates for typical rocketry usages.

The improved composition of the invention contains amm'onium nitrate as the major component. The ammonium nitrate may be either ordinary commercial ammonium nitrate such as is used for fertilizers. This commercial grade material contains a small amount of impurities and the particles are usually coated with moisture resisting material such as parafiin wax. Military grade ammonium ni trate which is almost chemically pure, is particularly suitable. The ammonium nitrate is preferably in a finely divided particulate form which may be either produced by pulling or by grinding. The ammonium nitrate is the major component of the composition and usually the composition will contain between about 65 and 80% of ammonium nitrate.

In order to permit the shaping of the ammonium nitrate composition into definite configurations a matrix former or binder material is present. When ammonium nitrate decomposes free-oxygen is formed. Advantage of the existence of this free-oxygen is taken and oxidizable material are used as the binders. These oxidizable organic materials may contain only carbon and hydrogen, for example, high molecular weight hydrocarbons such as asphalts or residuums, and rubbers either natural or synthetic. Or, the oxidizable organic material may contain other elements in addition to carbon and hydrogen for example, Thiokol rubber and neoprene. The stoichiometry of the composition is improved, with respect to smoke production, by the use of oxygenated organic materials as the binders. The binder or matrix former may be a single compound such as a rubber or asphalt or it may be a mixture of compounds. The mixtures are particularly suitable when special characteristics are to be imparted to the grain which cannot be obtained by the use of a single compound.

The multi-component hinder or matrix former commonly consists of a polymeric base material and a plasticizer therefor. Particularly suitable polymeric base materials are the polyvinyl resins such as polyvinylchloride and polyvinyl acetate; cellulose esters of alkanoic acids containing from 2 to 4 carbon atoms such as cellulose acetate, cellulose acetate butyrate and cellulose propionate are good bases; styrene acrylonitrile is an example of a copolymer which forms a good base material. In general the binder contains between about 15 and 45% of the particular polymeric base material.

The plas-ticizer component of the binder is broadly defined as an oxygenated hydrocarbon. The hydrocarbon base may be aliphatic or aromatic or may contain both forms. The oxygen may be present in the plasticizer in ether linkage and/or hydroxyl group and/ or carboxyl groups; also the oxygen may be present in inorganic substituents, particularly nitro groups. In general any plasticizers which are suitable for work with the defined polymers may be used in the invention.

Exemplary classes of plasticizers which are suitable are set out below. It is to be understood that these classes are illustrative only and do not limit the types of oxygenated hydrocarbons which may be used to plasticize the polymer.

Di-lower alkyl-phthalates, e.g. dimethyl phthalate, dibutyl phthalate dioctyl phthalate and dimet-hyl nitrophthalate.

Nitrobenzenes, e.g. nitrobenzene, dinitrobenzene, nitrotoluene, di-nitrotoluene, nitroxylene, and nitrodiphenyl.

Nitrodiphenyl ethers, e.g. nitrodiphenyl ether and 2,4-dinitrodiphenyl ether.

Tri-lower alkyl-cit-rates, e.g. trie'thyl citrate, tributyl citrate and triamyl citrate.

Acyl tri-lower alkyl-citr-ates where the acyl group contains 2-4 carbon atoms, e.g. acetyl triethyl citrate and acetyl tributyl citrate.

Glycerol-lower alkanoates, e.g. monoacetin, triacetin, glycerol, tripropionate and glycerol tributyrate.

Lower alkylene-glycol-lower al-kanoates wherein the glycol portion has a molecular weight below about 200, e.g. ethylene glycol diacetate, triethylene glycol dihexoate, triethylene glycol dioctoate, polyethylene glycol dioctoate, dipropylene glycol diaceta-te, ni-tromethyl propanediol diacetate, hydroxyethyl acetate and hydroxy propyl acetate (propylene glycol monoacetate).

Dinitrophenyl-l-ower alkyl-lower alkanoates, e.g. dinitrophenyl ethylacetate, and dinitrophenyl amyloctoate.

Lower alkylene-glycols wherein the molecular weight is below about 200, e.g. diethylene glycol, polyethylene glycol (i200), and :tetrapropylene glycol.

Lower alkylene-glycol oxalates, e.g. diethylene glycol oxalate and polyethylene glycol (200) oxalate.

Lower alkylene-glycol maleates, e.g. ethylene glycol maleate, and

Bis-(diethylene glycol monoethyl ether) maleate.

Lower alkylene-glycol diglycolates, e.g. ethylene glycol diglycolate and diethylene glycol diglyc-olate.

Miscellaneous diglycollates, e.g. dibutyl diglycollate, di-

methylalkyl diglycollate and me-thylcarbitol diglycollate.

Lower alkyl-phthalyl-lower alkyl-glycollate, e.g. methyl phthalyl ethyl glycollate, ethyl phthalyl ethyl glyc-ollate and butyl phthalyl butyl glycollate.

Nitrophenoxy alkanols wherein the ialkanol portion is derived from a glycol having a molecular weight of not more than about 200. These may be pure compounds or admixed with major component bis (nitrophenoxy)- alkane.

A single plasticizer may be used or more usually, two or more plasticizers may be used in conjunction. The particular requirements with respect to use Will determine not only the polymer but also the particular plasticizer or combination of plasticizers which are used.

In addition to the basic components, i.e. ammonium nitrate binder and catalyst system, the gas-generator propellant composition may contain other materials. For example, materials may be present to improve low temperature :ignitability, for instance oximes may be present or, asphalt may be present. Surfactants may be present in order to improve the coating of the nitrate with the binder and to improve the shape characteristics of the composition.

The aromatic hydrocarbon amines are known to be gas evolution stabilization additives. Examples of these aromatic amines are toluene diamine, diphenyl amine, naphthalene diamine, and toluene triamine. In general the :aromatic hydrocarbon amines are used in amounts between about 0.5 and 5 percent. While these aromatic hydrocarbon amines are effective, for severe duties they are frequently not sufficiently eifective alone.

Test

The composition to be tested for burning rate, pressure exponent and other characteristics required by military specifications was prepared by first forming a homogeneous viscous liquid binder at a temperature of about 130 C. Polyvinyl acetate was the polymer base, 40% based on binder. The plasticizers were "(21) 2,4-dinitrodiphenyl ether, :(b) dinit-rophenylpropyl ether, 30% and (c) triethylene glycol dihexoate, 20%. The binder was then cooled to about 100- C. and the ammonium nitrate in fine particles, carbon black and magnesium oxide were blended into the binder until a pasty mass was formed. At this time insoluble *Prussian blue and N-aminopropylmorpholine were introduced into the mixture and worked into the mass of material.

The homogeneous pasty mass was xtruded as rods suitable for use in burning rate tests. The

burning rate tests were conducted in a Crawford bomb pressured with nitrogen at 1000 p.s.i. and 25 C. temperature.

The composition of the invention consisted of binder,

12%, carbon black 3%, magnesium oxide l%, amrnonium nitrate 7 8%, Prussian blue 3% and N-aminopropylmorph-oline 3% This composition had a burning rate of 0.24 inch per second and a pressure exponent 0150.42. Another composition identical to the one above except 1 that 3% of ammonium nitrate was substituted for the N-aminopropylmorpholine was made; this had a burning rate of 0.17 inch per second.

Thus having described the invention, what is claimed is:

1. A composition consisting essentially of between about 0.5 and 8 weight percent of a Prussian blue, between about and 8 weight percent of an N-aminoalkylmorpholine having 1-4 carbon atoms in the alkyl portion, ammonium nitrate as the predominant component and between about l0 and 40 weight percent of oxidizable organic binder consisting of a polymeric base selected from the class consisting of cellulose esters of alkanoic acids containing from 2 to 4 carbon atoms, polyvinyl chloride, polyvinyl acetate, and styrene-acrylonitnile, and an oxygenated hydrocarbon plasticizer therefor.

2. The composition of claim 1 wherein said morpholine is N-aminopropylmorpholine.

"3. A composition consisting essentially of ammonium nitrate as the predominant component, between about 1 and 6 weight percent of a Prussian blue, between about 1 No references cited.

CQLRL D. QUARLFORTH, Primary Examiner. LEON D. ROSDOL, Examiner. 

1. A COMPOSITION CONSISTING ESSENTIALLY OF BETWEEN ABOUT 0.5 AND 8 WEIGHT PERCENT OF A PRUSSIONA BLUE, BETWEEN ABOUT 0.5 AND 8 WEIGHT PERCENT OF AN N-AMINOALKYLMORPHOLINE HAVING 1-4 CARBON ATOMS IN THE ALKYL PORTION, AMMONIUM NITRATE AS THE PREDOMINANT COMPONENT AND BETWEEN ABOUT 10 AND 40 WEIGHT PERCENT OF OXIDIZABLE ORGANIC BINDER CONSISTING OF A POLYMERIC BASE SLECTED FROM THE CLASS CONSISTING OF CELLULOSE ESTERS, OF ALKANOIC ACIDS CONTAINING FROM 2 TO 4 CARBON ATOMS, POLYVINYL CHLORIDE, POLYVINYL ACETATE, AND STYRENE-ACRYLONITRILE, AND AN OXYGENATED HYDROCARBON PLASTICIZER THEREFOR. 